Computer files store information to be used by a computer. Such files are normally stored in nonvolatile storage devices, such as hard disks. As the storage devices are subject to failure, many computer files are backed up, by copying the files, in whole or in part, to another device (sometimes called “secondary storage”), such as an additional hard disk. During a full back up, a complete copy of a computer file is made. However, when the total number and size of the full backup files becomes too large, it becomes desirable to make just incremental back ups, wherein only changes from the last full back up (or the last incremental back up) are recorded.
Back ups of the type described above may be performed periodically, e.g. incremental back ups every hour, and/or full back ups every night. Over time, backup files in secondary storage eventually grow in size and/or number such that the secondary storage begins to fill up. If the secondary storage does fill up, no more backup files can be stored therein, and hence no back up can be done, unless some backup files are deleted from the secondary storage. Typically, a user manually performs another back up, this time back up files currently in the secondary storage are backed up to yet another device (sometimes called “tertiary storage”), typically removable media such as a magnetic tape or an optical disk. The user must then delete the manually backed up files from secondary storage, to make room for new backup files that are to be generated by periodic back up.
Inventors of the current invention (described below) note that the above-described process requires a user to be knowledgeable about the location (e.g. a specific directory or folder), and the names of the back up files to be transferred to tertiary storage and/or deleted. Depending on the size, complexity and/or documentation of the computer system, becoming knowledgeable about the location and names of backup files may be a non-trivial task for most users. Moreover, the above-described manual process of transferring and/or deleting backup files is labor intensive and error prone. For example, if a user decides to delete all files older than a specific date (or to simply delete the oldest file), the user may delete a file that happens to be the last full back up, and without which all incremental back up files of a later date cannot be used. Accordingly, the inventors believe that there is a need for automated deletion of backup files.
Deletion of files (regardless of their type and content) is performed automatically by a prior art feature called “recycle bin” in the operating system “WINDOWS 2000” available from MICROSOFT CORPORATION. The recycle bin, when in use, holds all items that have been manually deleted by a user, from a hard disk in the user's personal computer. Items in the recycle bin remain therein by default until the user manually empties the recycle bin. The user can set a parameter, called “maximum size” of the recycle bin, as a percentage of the total space on the hard disk, which limits the amount of space the recycle bin can use. When the recycle bin fills up, Windows 2000 automatically cleans out enough space in the recycle bin to accommodate storage of more recently deleted files. Windows 2000 apparently deletes files from the recycle bin in a fixed in-built order that is embedded deep within the operating system, and not accessible to the user. Note that to use the recycle bin, the user has to manually mark a file as being deleted (or move the file to the recycle bin) in order for the file to be eligible for being cleaned out by the recycle bin.